1. Field of the Invention
Embodiments of the invention generally relate to controlling plasma uniformity in a semiconductor process.
2. Background of the Related Art
Plasma reactors are regularly utilized in various semiconductor processes, such as etching processes, chemical vapor deposition processes, and other processes related to the manufacture of semiconductor devices. An inductively coupled RF plasma reactor typically has an inductive coil antenna wound around the reactor chamber and connected to a plasma source RF power supply. An inductively coupled RF plasma reactor facilitates generation of high plasma ion density, which is beneficial for obtaining high production throughput, while also avoiding a concomitant increase in ion bombardment damage to a substrate being processed.
Conventional inductively coupled plasma reactors have a plasma ion density distribution across the surface of the substrate being processed that varies greatly depending upon various processing parameters. These processing parameters, for example, may include the quantity and/or type of process gas or gas mixture introduced into the reactor chamber. The plasma ion density may be high at the substrate center and low at the substrate periphery for one process gas, while for another process gas the plasma ion density may be low at the substrate center and high at the substrate periphery. As a result of these types of processing characteristics, conventional plasma reactor RF coil designs are customized for each process or process gas in order to provide a specific plasma uniformity across a substrate surface in the reactor. More than one RF coil, typically two coils, have also been implemented in order to improve plasma uniformity in the processing chamber. In this configuration, the first RF coil is in electrical communication with a first power supply through, for example, a first matching network/circuit, while the second RF coil is in electrical communication with a second RF power supply through a second matching network/circuit. Therefore, the respective RF power supplies and accompanying matching networks operate to individually control the power supplied to the respective coils.
FIG. 1 illustrates a cross sectional view of a typical plasma processing chamber having two RF coils disposed on a lid of the chamber. The plasma processing chamber generally includes a vacuum chamber 10 having a generally cylindrical side wall 15 and a dome shaped ceiling 20. A gas inlet tube 25 supplies process gas, which may be chlorine for etch processing, for example, into the chamber 10. A substrate support member or substrate pedestal 30 supports a substrate, such as semiconductor substrate 35, inside the chamber 10. An RF power supply 40 is also typically connected to the pedestal 30 through a conventional RF impedance match network 45. A plasma is ignited and maintained within the chamber 10 above substrate support 30 by RF power inductively coupled from a coil antenna 50 consisting of a pair of independent (electrically separate) antenna loops or RF coils 52, 54 wound around different portions of the dome-shaped ceiling. In the embodiment shown in FIG. 1, both loops are wound around a common axis of symmetry coincident with the axis of symmetry of the dome-shaped ceiling 20 and the axis of symmetry of the substrate pedestal 30 and substrate 35. The first RF coil 52 is wound around a bottom portion of the dome-shaped ceiling 20 while the second RF coil 54 is positioned centrally over the ceiling 20. First and second RF coils 52, 54 are separately connected to respective first and second RF power sources 60, 65 through first and second RF impedance match networks 70, 75. RF power in each RF coil 52, 54 is separately controlled. The RF power signal applied to the first RF coil (bottom/outer antenna loop) 52 predominantly affects plasma ion density near the periphery of the substrate 35 while the RF power signal applied to the second RF coil (top/inner antenna loop) 54 predominantly affects plasma ion density near the center of the substrate 35. The RF power signals delivered to each of the RF coils are adjusted or configured relative to each other to achieve substantial uniformity of plasma ion distribution over a substrate disposed on a substrate support member.
In operation, the plasma processing system receives a substrate 35 on substrate support member 30 for processing in chamber 10. Chamber 10 may then be pulled to a predetermined pressure/vacuum by a vacuum pump system (not shown). Once the predetermined pressure is achieved, a process gas may be introduced into the chamber 10 by gas inlet tube 25, while the vacuum pumping system continues to pump the chamber 10, such that an equilibrium processing pressure is obtained. The processing pressure is adjustable through, for example, throttling the communication of the vacuum system to the chamber 10 or adjusting the flow rate of the process gas being introduced into chamber 10 by gas line 25. Once the pressure and gas flow are established, the respective power supplies may be activated. Thus, power is independently supplied to the inner coil 54, outer coil 52, and the substrate support member 30. The application of power to the coils 52 and 54, which is generally RF power, facilitates striking of a plasma in the region immediately above the substrate support member 30. The ion density of the plasma may be increased or decreased through adjustment of the power supplied to the coils 52 and 54 or through adjustment of the processing pressure in chamber 10, i.e., through increased/decreased flow rate of the process gas or an increase/decrease in the chamber pumping rate.
During conventional semiconductor processing methods, the ion density generally remains constant over the surface of the substrate during a substrate processing sequence. This is undesirable for some processing sequences, as the plasma uniformity over the surface of the substrate generated by a particular processing chamber may be acceptable for one portion of a sequence, while causing substrate damage during another portion of the sequence. Conventional processing chambers may vary the ion density and uniformity by varying pressure in the chamber (the density or flow of the process gas into the chamber) or the power applied to the coils. However, varying the gas flow and/or power applied to the coils is also undesirable, as varying these parameters affects also affects the plasma composition, which is desired to remain constant through a processing sequence.
Another disadvantage of conventional processing systems is that the addition of an independent RF power source and associated RF impedance match network for each RF coil increases the equipment and operation costs for each additional RF coil utilized on a processing chamber. This directly results in an increased cost for processing substrates. Furthermore, the independent RF source and matching network configuration presents difficulties in matching the impedance of the respective coils, which leads to more difficulties in controlling the plasma power delivered to each of the coils.
Other conventional apparatuses have attempted to control plasma power in an inductively coupled plasma reactor having multiple coils utilizing a plurality of high power relays for switching connection from the power source to each of the coils. However, these switching mechanisms do not provide efficient operation of the coils, do not provide sufficient control of the power delivered to each of the coils on a continual basis, and have been difficult to build.
Therefore, in view of the disadvantages of conventional systems, there is a need for an improved apparatus and method for controlling plasma uniformity, wherein the apparatus and method allows for plasma uniformity adjustment without adjusting conventional processing parameters.
Embodiments of the invention generally provide a method for processing a semiconductor substrate, wherein the method includes positioning a substrate in a processing chamber having at least a first and second coils positioned above the substrate and supplying a first electrical current to the first coil. The method further includes supplying a second current to the second coil and regulating a current ratio of electrical current supplied to the first and second coils with a power distribution network in communication with the first and second coils and a single power supply.
Embodiments of the invention further provide a method for controlling plasma uniformity in a semiconductor processing chamber, wherein the method includes positioning a first coil above the processing chamber, the first coil being concentrically positioned about a vertical axis of the processing chamber, and positioning a second coil above the processing chamber, the second coil being concentrically positioned about the vertical axis of the processing chamber and radially outward from the first coil. The method further includes supplying electrical power to the first and second coils with a single power distribution network to selectively regulate a magnetic field intensity generated by the first and second coils above a workpiece in the processing chamber.
Embodiments of the invention further provide a method for varying plasma uniformity in a semiconductor processing chamber having at least a first and second coils positioned above the chamber. The method generally includes supplying a first electrical current to the first coil, supplying a second electrical current to the second coil, and varying a capacitive element in a power distribution network to control a ratio of the first electrical current to the second electrical current.